1. Field of the Invention
The present invention relates to an electronic apparatus with an electronic device such as an infrared detector in an infrared temperature detecting apparatus or a superconducting microwave circuit apparatus, which is used with an electronic device which is accommodated in a vacuum case and equipped with an electronic circuit which is operated in a state of being cooled to a temperature of 150 K. or less, more specifically to a structure for cooling the electronic device in such electronic apparatus.
2. Description of the Related Art
Conventionally, an electronic device having an electronic circuit which is operated in a low temperature environment, more specifically at a temperature of 150 K. or less, e.g. at a cryogenic temperature between 4 K. and 150 K. close to the liquid nitrogen temperature (about 77 K.) and the liquid helium temperature (about 4 K.), respectively, such as an infrared detector in an infrared temperature detecting apparatus or a superconducting microwave circuit apparatus, constitutes an electronic apparatus in such a manner that the electronic device is mounted on a mounting portion of an electronic device case comprising a vacuum heat insulation housing in which cooling means having a cooling structure and the mounting portion for the electronic device, which cooling means is called a cold head, is disposed, so as to be accommodated in the vacuum heat insulation housing and the electronic device is connected to an external circuit. The electronic device is used under constant temperature and environment conditions by operating the electronic circuit while the electronic device is cooled to a desired low temperature by the cooling structure.
FIG. 7 is a section view showing an example of such prior art electronic apparatus. In FIG. 7, a vacuum heat insulation housing 1 accommodates a cold head 2 which constitutes cooling means together with a refrigerator or the like, and an electronic device 4 is provided with an electronic circuit 3 operated at a temperature between 4 K. and 150 K. The electronic device 4 is directly mounted on the cold head 2 of the cooling means to be accommodated in the vacuum heat insulation housing 1.
A vacuum sealed housing-side input/output connector 5 is provided so as to penetrate a housing wall of the vacuum heat insulation housing 1. An input/output coaxial connector 6 is attached to the electronic device 4 and electrically connected to the electronic circuit 3. A cable 7 electrically connects the housing-side input/output connector 5 and the input/output coaxial connector 6, and a cable 7' electrically connects an external electric circuit and the housing-side input/output connector 5.
In the conventional electronic device input/output of an electrical signal between the external electric circuit and the electronic device 4 in the electronic apparatus is executed via the cable 7', the housing-side input/output connector 5, cable 7 and the input/output coaxial connector 6, and the electronic circuit 3 is operated under cooled condition by cooling a bottom surface of the main body of the electronic device 4 by the cold head 2 connected with the refrigerator.
FIGS. 8A to 8C show front views and side views of the housing-side input/output connector 5, the input/output coaxial connector 6 and the cable 7, respectively. These drawings allocate a front view in the center and side views of both sides on both sides of the front view. In FIG. 8C, a section view of a central portion of the front view is also shown.
In the housing-side input/output connector 5 shown in FIG. 8A, outer conductors 8, 8' are ground-side conductors, central conductors 9, 9' transmit electrical signals, and dielectrics 10, 10' interposed between the outer conductors 8, 8' and the central conductors 9, 9' hold the central conductors 9, 9' to electrically insulate both conductors. Female connectors 11 are connected to the cables 7, 7' at the inside and outside of the vacuum heat insulation housing 1, and a gasket 12 is pressed on the housing wall of the vacuum heat insulation housing 1 to execute vacuum sealing.
In the input/output coaxial connector 6 shown in FIG. 8B, outer conductors 13, 13' are ground-side conductors, central conductors 14, 14' transmit electrical signals, and dielectrics 15, 15' interposed between the outer conductors 13, 13' and the central conductors 14, 14' hold the central conductors 14, 14' to electrically insulate both conductors. A female connector 16 is connected to the cable 7.
In the cable 7 shown in FIG. 8C, outer conductors 17, 17' are ground-side conductors, central conductors 18, 18' transmit electrical signals, and dielectrics 19, 19' interposed between the outer conductors 17, 17' and the central conductors 18, 18' hold the central conductors 18, 18' to electrically insulate the central and outer conductors. A male connector 20 is connected to the housing-side input/output connector 5 or the input/output coaxial connector 6. The cable 7' has almost the same constitution.
As shown in FIGS. 8A to 8C, any of the housing-side input/output connector 5, the input/output coaxial connector 6, and the cable 7 in the conventional electronic apparatus are constructed of the central conductors 9, 9', 14, 14', 18, 18' and the dielectrics lo, 10', 15,15', 19, 19' holding the central conductors, although there are differences of whether or not the dielectrics are surrounded by the outer conductors.
In the above described conventional electronic apparatus, however, dielectric materials having a good electrical insulation property and a poor heat conductivity, such as polymeric materials, e.g. tetrafluoro ethylene resin (having a heat conductivity of about 0.3 W/m.multidot.K.) are used in producing the dielectrics 10, 10', 15, 15', 19, 19' of the housing-side input/output connector 5, input/output coaxial connector 6, and the cable 7 because such dielectric materials have low dielectric constants and are easily worked and fabricated into a desired object. On the other hand, such polymeric materials have very poor heat conductivity, so that the ability of heat radiation from the central conductors 9, 9', 14, 14' is very poor, when such polymeric materials are used for the dielectrics 10, 10', 15, 15'.
Accordingly, even if the electronic device 4 is cooled by the cold head 2 in the vacuum heat insulation structure, heat is transmitted from the outside of the electronic apparatus via the central conductors 9, 9' of the housing-side input/output connector 5 and the central conductors 18, 18' of the cable 7 to the electronic circuit 3 in the electronic device 4 because of low cooling efficiencies of the central conductors 14, 14' held by the dielectrics 15, 15' in the input/output coaxial connector 6, and as a result, it becomes difficult to cool the electronic device 4 efficiently and sufficiently, and a problem that a stable operation of the electronic circuit 3 is difficult due to the temperature distribution generated on it.
FIG. 9 is a perspective view showing a heat flow into the electronic device 4 through the input/output coaxial connector 6. In FIG. 9, the same elements as in FIGS. 7 and 8 are denoted by the same reference numerals, and a dotted arrow denotes the heat flow.
As shown in FIG. 9, in the case of the electronic device 4 of the conventional electronic apparatus, since the heat conductivity of the dielectric 15 of the input/output coaxial connector 6 is poor, the heat having passed through the central conductor 14 from the outside is not radiated to the outside through the dielectric 15 but passes through the central conductor 14 as it is to reach the electronic circuit 3 and diffuse in the electronic circuit 3.
In the conventional electronic apparatus as mentioned above, even if the electronic device 4 is configured to be a vacuum heat insulation structure and then the electronic device 4 is cooled, the heat inflow from the outside is transmitted through the central conductor 14 to flow in to the electronic device 4 because of the low cooling efficiency of the central conductor 14 of the connector 6, which brings a temperature distribution in electronic circuit 3 and a local temperature rising within the electronic circuit 3.
Therefore, a problem arises that the characteristics of the electronic circuit 3 as initially designed cannot be obtained. Particularly, in the case where the electronic device 4 that is used in a state of being cooled to a very low temperature such as the liquid nitrogen temperature has the electronic circuit 3 made of a superconducting film, a local temperature rising destroy the superconducting condition, which causes the characteristics of the electronic circuit 3 to be significantly degraded.